For example, in a broadcast receiver for receiving a television broadcast or an information reproducer for reproducing recorded information from an information recording medium, when reproducing an audio signal from the received broadcast signal or the read-out signal, a sound quantity control process is applied to the audio signal to improve sound quality.
Contents of the sound quality control process applied to the audio signal is changed according to whether the audio signal is a speech signal such as human speaking voice or a music (non-speech) signal such as a musical composition. Generally, sound quality in a speech signal can be improved by emphasizing and clarifying center localizing signal components in a talk scene, a live sports broadcast, etc., whereas sound quality in a music signal can be improved by emphasizing a stereophonic effect and enlarging the soundspace.
Therefore, whether the acquired audio signal is a speech signal or a music signal is determined, and then, a corresponding sound quality control process is applied to the audio signal in accordance with the determination result. For example, in JP-H07-013586-A, the number of zero-crossing points, power change, etc. in an input acoustic signal are analyzed to determine the acoustic signal as one of the three types, i.e. “speech”, “non-speech (music)” and “indefinite”, and frequency characteristic for the acoustic signal is controlled stepwise based on the determination result.
This control method uses an equalizer having stepwise different band emphasizing characteristics in a range of from frequency characteristic for emphasizing a speech band for “speech” to flat frequency characteristic (wider band than the speech band only) including a non-speech band for “non-speech (music)” in order to obtain stepwise transition of frequency characteristic based on the determination result so that the frequency characteristic is changed to speech characteristic for “speech” or flat characteristic for “non-speech (music)” or the previous determination is kept for “indefinite”.
However, in an ordinary broadcast program, a scene explicitly composed of only speech or of only non-speech (music) is rare. Accordingly, a mixed signal is apt to be judged to be “indefinite”, or previous misjudgment is apt to be kept to continuously cause mistaken sound quality control. Moreover, although a low power signal section such as background noise, BGM, etc. is generally not important, since determination is not made in accordance with the signal power value, followability of sound quality control to a change in signal characteristic after judgment when the ordinary judgment is applied to such low power signal section.